It's not a sad sight, it's a scary sight!
Surprisingly many bikes actually burn down, on many reasons: whether it's some dry stuff near to hot exhaust (i.e. riding over dryed out field or some dry woody offroad), bad electrical connections especially the detoriarated spark cables with strong voltage capability, hot brake disks ignite tar dust, or the worst - fuel vapor from vent hoses fire up in very hot weather.
If it catches fire - oh boy can bikes burn! Like a wood-stick quickly and intensly they burn!!! Especially those with lot of plastic. I've seen it too on a moped.
On my previous Suzuki sportsbike the electricity because of the bad OEM wiring started to throw sparks UNDER THE FUEL TANK! Goosh, it was a scary sight. Managed to cut the engine out in the right time tho.
This all really makes me think to carry a small compact fire extinguisher on the bike somewhere in accessible place.
If you get to it in the right time you'll be OK, if not, there isn't much you can do...
